cmake: fix sat/java/CMakeLists.txt

note:
* need to introduce a new target `java_cp_model_proto` which depends on the
custom cmd generating the java/cp_model_proto.swig
* then use SWIG_MODULE_jnicp_model_proto_EXTRA_DEPS to force generation of it.
ref: https://cmake.org/cmake/help/latest/module/UseSWIG.html#cmake-variables

Author: Mizux

ortools/sat/java/CMakeLists.txt

@@ -42,19 +42,29 @@ elseif(UNIX)
 endif()
 
 add_custom_command(
-  OUTPUT "${CMAKE_CURRENT_BINARY_DIR}/cp_model_proto.swig"
+  OUTPUT ${CMAKE_CURRENT_BINARY_DIR}/java_cp_model_proto_timestamp
   COMMAND gen_sat_java_swig > "${CMAKE_CURRENT_BINARY_DIR}/cp_model_proto.swig"
+  COMMAND ${CMAKE_COMMAND} -E touch ${CMAKE_CURRENT_BINARY_DIR}/java_cp_model_proto_timestamp
   DEPENDS gen_sat_java_swig
-  COMMENT "Generate cp_model_proto.swig"
+  BYPRODUCTS
+    ${CMAKE_CURRENT_BINARY_DIR}/cp_model_proto.swig
+  COMMENT "Generate java/cp_model_proto.swig (java_cp_model_proto_timestamp)"
   VERBATIM)
 
+add_custom_target(java_cp_model_proto
+  DEPENDS
+    ${CMAKE_CURRENT_BINARY_DIR}/java_cp_model_proto_timestamp
+  WORKING_DIRECTORY ${CMAKE_CURRENT_BINARY_DIR})
+
 # cp_model_proto
 set_property(SOURCE "${CMAKE_CURRENT_BINARY_DIR}/cp_model_proto.swig" PROPERTY CPLUSPLUS ON)
 set_property(SOURCE "${CMAKE_CURRENT_BINARY_DIR}/cp_model_proto.swig" PROPERTY SWIG_MODULE_NAME cp_model_proto)
 set_property(SOURCE "${CMAKE_CURRENT_BINARY_DIR}/cp_model_proto.swig" PROPERTY COMPILE_DEFINITIONS
   ${OR_TOOLS_COMPILE_DEFINITIONS} ABSL_MUST_USE_RESULT=)
 set_property(SOURCE "${CMAKE_CURRENT_BINARY_DIR}/cp_model_proto.swig" PROPERTY COMPILE_OPTIONS
   -package ${JAVA_PACKAGE}.sat)
+
+set(SWIG_MODULE_jnicp_model_proto_EXTRA_DEPS java_cp_model_proto)
 swig_add_library(jnicp_model_proto
   TYPE OBJECT
   LANGUAGE java